Usa array que para eso son,
http://www.marcofbb.com.ar/vectores-...reglos-en-php/ http://php.net/manual/en/language.variables.php
Código PHP:
Ver original<?php
$arg = "foo";
$val = "bar";
//${$arg$val} = "in valid"; // Invalid
${$arg . $val} = "working";
echo $foobar; // "working";
//echo $arg$val; // Invalid
//echo ${$arg$val}; // Invalid
echo ${$arg . $val}; // "working"
?>